Impact of High Voltage Shunt Capacitor Banks on General Purpose Circuit Breakers

Transcription

1 a b a b Impat of High Voltage Shunt Capaitor Banks on General Purpose Ciruit Breakers M. Alawie *, Y. Filion, A. Coutu Abstrat It is well known that during a fault on a bus bar with the presene of a shunt apaitor bank, a large part of the transient urrent meant to be interrupted by a bus bar or a line general purpose iruit breaker in the ase of a reignition omes from the disharge of the apaitor bank. This high frequeny urrent, a few khz, is known as the Outrush urrent. This partiular duty an exeed the appliable iruit breakers standards (IEC or IEEE C7.06) in terms of equivalent produt of urrent frequeny of x0 7 A.Hz defined for general purpose CB and even the 8,5x0 7 A.Hz defined for definite purpose CB. Also, an attempt of interruption at eah zero rossing of this high frequeny urrent for some tehnologies of iruit breaker an lead to a voltage esalation and in the worst ase, the destrution of the iruit breaker. In this paper we will explore by simulation, using EMTP-RV, the impat of different onfigurations of shunt apaitor on general purpose iruit breakers using grounded and ungrounded shunt apaitor bank, also damping reator on the neutral side of the shunt apaitor bank with varistors in parallel. Keywords: Shunt apaitor bank, Outrush urrent, Ciruit breaker (CB), Reignition, damping reator, Grounding, Transients, Transient Reovery Voltage (TRV), Rate of Raise of Reovery Voltage (RRRV), Power System, EMTP-RV. II. SCENARIO DESCRIPTION We have hosen a 0 kv substation as subjet of this study. Figure illustrates the 0 kv substation whih is equipped with ungrounded Wye onneted shunt apaitor banks of 04 MVAR eah. It should be noted that no filtered bank has been onsidered in the explored onfigurations. CB Reignition Terminal fault Fault CB a FD XC 04 MVAR 75 kv soure with impednae Short iruit level : 40 ka 4 Transformers 75/0 kv YgYgD 9%@00MVA FD XC 04 MVAR FD XC 04 MVAR 0 kv bus bar 00 meter 0.6mH Séries reator 0.6 mh Q = Overhead Lines with load Fig. EMTP-RV equivalent iruit of a 0 kv substation equipped with ungrounded shunt apaitor banks S I. INTRODUCTION HUNT apaitor banks are widely used on power systems to provide reative power lose to the load enters. The installation of shunt apaitor banks on a power system has benefiial effets suh as the voltage regulation and the redution of the losses of ative power to be transmitted. On the Hydro-Quebe transmission system the shunt apaitor banks represent more than 00 MVAR distributed mainly on four levels of transmission voltages: 67 MVAR on the 69 kv level, 5400 MVAR on 0 kv level, 70 MVAR on 0 kv level and 580 MVAR on 5 kv level. The size of an individual shunt apaitor bank starts at 8 MVAR on the 69 kv level and goes up to 84 MVAR on the 5 kv level. Most of these shunt apaitor banks are ungrounded exept for the 5 kv levels where all banks are grounded to redue the insulation level of the neutral and also to redue the RV onstraint on the iruit breaker of the shunt apaitor bank. (*) Mohamad Alawie, orresponding author, is with System Studies, Hydro- Québe TransÉnergie Complexe Desjardins, Tour de l Est, 0e étage, ase postale 0000, Montréal (Q), Canada, H5B-H7. Phone: (Ext. 568). Fax: alawie.mohamad@hydro.q.a Y. Filion is also with System Studies, Hydro-Québe TransÉnergie. A. Coutu is also with System Studies, Hydro-Québe TransÉnergie. Paper submitted to the International Conferene on Power Systems Transients (IPST0) in Delft, Netherlands June 4-7, 0. As shown in Fig., eah shunt apaitor bank is equipped with 0.6 mh damping reator with a quality fator (Q) of used to limit inrush urrent during energization. We have onsidered a bus bar distane of 00 meters between eah shunt apaitor bank and the main bus bar. This substation feeds an 00 MVA load through 5 overheads lines represented by a onstant parameters line model ( line). The power autotransformers, number of 4, are 75/0 kv and YgYgD onneted with 9% of impedane based on 00MVA. The power system is represented by a 75 kv soure with impedane to reflet a short iruit level of 40 ka. In the next setions the influene of the onfiguration of the shunt apaitor banks will be studied during the interruption of a phases and phase fault to ground (terminal fault) by a general purpose iruit breaker. We will further simulate, for eah onfiguration, a multi-phase reignition [,] at the peak TRVs and observe the impat on the outrush urrent seen by the iruit breaker. III. UNGROUNDED WYE CONNECTED SHUNT CAPACITOR BANK A. Case of phases to ground fault In this ase we produe a phase to ground fault (terminal fault) on the main bus bar that we lear some yles later. We obtain a maximum TRV of.6 p.u. (i.e. p.u. = 87, kv

2 peak for a 0 kv system) on phase A of the CB as shown in Figure. RRRV in this ase is less than 0.5 kv/µse. The TRV of,5 p.u. observed on phase C exeeds largely the standard value of.8 p.u. in appliable standards [5] so we further simulated a multi-phase reignition on phase A and C. Severe urrents and additional high frequeny urrent zeros were found to be far beyond the values given in appliable standards. Figure 5 shows learly a peak value of 90 ka for phase A and 0 ka for phase C with a frequeny of almost KHz. Fig. TRV observed on eah phase of the iruit breaker during phases fault interruption Thereafter a reignition has been simulated on the peak TRV of phase A; whih resulted in a TRV on phase B and C of the CB in the order of,0 and,5 p.u. respetively as shown in Figure. Fig.5 Current observed on phase A and C after a multi-phase reignition Fig. Transient voltage observed on phase B and C of the CB after a reignition on phase A phases fault The urrent observed on phase A is lose to 70 ka peak with a frequeny of 700 Hz as shown in Figure 4. Fig.4 Current observed on phase A after a first reignition In fat this urrent is a ombination of two omponents; a 60 Hz omponent oming from phase A of the soure and a 700 Hz omponent representing the disharge of phases A, B and C of the shunt apaitor bank in the fault. The high frequeny of the urrent an be simply explained by the resonane frequeny between the shunt apaitor bank and the damping reator where they follow the natural frequeny of an LC iruit given by: f LC The multiple zero rossing in the breaker reignition urrent an be explained by the fat that this urrent is the sum of a high frequeny urrent whih is the disharge of the shunt apaitor banks (outrush) and the short iruit urrent of the soure. A zero rossing urrent result when the urrent disharge is higher then the short iruit urrent of the soure whih is the ase. These high urrent and frequeny values reate a hydrodynami ho wave, whih represent a mehanial onstraint espeially for oil iruit breakers. Furthermore, test urrent and frequeny reommended values aording to the standards, equivalent produt, are for a total limit of x0 7 A.Hz. for general purpose CB. In this ase the value obtained by simulation as shown in Figure 5 is 8 x0 7 A.Hz, largely exeeded the value aording to the standards even for a definite purpose CB (8 x0 7 A.Hz). It is also of note that some tehnologies of CB suh MOCB (Minimum Oil Ciruit Breaker) an attempt to interrupt this high frequeny urrent leading to a voltage esalation following eah unsuessful interruption attempt[,8]; a situation that in the worst ase an result in the destrution of the iruit breaker. The size of the limiting reator has an important impat on two aspets of the disharge urrent of a shunt apaitor bank. The first aspet is the frequeny of the disharge urrent where inreasing the size of the limiting reator means dereasing the frequeny of the urrent. Also, inreasing the

3 size of the limiting reator means dereasing the peak value of the disharge urrent sine this urrent follow the given formula: I Peak E C L We have simulated the previous onfigurations with 4 different values for limiting reators: mh, mh,,5mh and 5mH. In ase of learing a phases to ground fault the maximum TRV obtained is redued from,6 p.u. on phase A in the original ase (with 0,6mH for damping reator) to:,5 p.u. in ase of mh,,4 p.u. in ase of mh and,5 p.u. in ase of,5mh and.48 p.u. in ase of 5mH. A first reignition on phase A give rise to TRV on phase B and C of : respetively,6 and,8 p.u. in ase of mh damping reator,,89 and, p.u. in ase of mh and,80 and,88 p.u. in ase of,5mh,,88 and,98 p.u. in ase of 5mH. The reignition urrents are similar in shape to Figure 4 with a peak value between 70 and 80 ka depending on the size of the damping reator. A multiphase reignition has been simulated on phases A and C. As we see in Figure 6 and 7 the peak value of the urrent and the frequeny dereased with the inreasing of the damping reator. We notie that with the use of 5 mh the produt frequeny urrent is around 5,4x0 7 A.Hz whih is still a lot higher than the onstraint for a general purpose CB, i.e. x0 7 A.Hz. Also, the zero rossing was not ompletely eliminated and we notie two zero rossing before the first natural zero. We ve notied also that in ase of 5mH the di/dt (00 A/µse) is mush lower than the original ase of 0.6mH (di/dt of 500 A/µse) inreasing the probability that a MOCB will attempt to interrupt a zero rossing urrent. Fig.7 Current observed on phase C for different values of damping reator after a multi-phase reignition B. Case of phase to ground fault In this ase as shown in Figure 8, the TRV observed on the faulted phase is,46 p.u. and the RRRV still less than 0,5 kv/µse. Fig. 8 TRV observed on eah phase of the iruit breaker after learing phase to ground fault The same simulations have been performed also in this ase with a reignition on the faulted phase. We observed a transient voltage in the magnitude of,4 p.u on phase C and,0 p.u. on phase B (see Figure 9). Fig.6 Current observed on phase A for different values of damping reator after a multi-phase reignition Fig.9 Transient voltage observed on phase C and B of the CB after a reignition on phase A The urrent is quite similar to the one obtained when we simulate a first reignition after learing a phases to ground

4 fault. The peak value is 70 ka with a frequeny of 700 Hz. Fig. TRV observed on eah phase of the iruit breaker With a reignition on the peak TRV of phase B; we obtained a transient voltage on phase A and C of the CB in the order of,5 and,4 p.u. respetively as shown in Figure. Fig.0 Current observed on phase A after a first reignition The simulations of multi-phase reignition proves as shown in Figure that no urrent will be observed on the seond phase (phase C in this ase). Fig. Transient voltage observed on phase A and C of the CB after a reignition on phase B We notie in this ase that the urrent observed on the phase B is around 90 ka peak value with a frequeny of.8 khz ombined to a multiple zero rossing as shown in Figure 4. Fig. Current observed on phase A and C after a multi-phase reignition IV. GROUNDED WYE CONNECTED SHUNT CAPACITOR BANK In this ase the neutral of the shunt apaitor bank will be simply onneted to earth. A. Case of phases to ground fault As shown in Figure, in this ase with phases to ground fault a maximum TRV of,7 p.u. is observed on phase B. RRRV in this ase is less than 0, kv/µse. Fig.4 Current observed on phase B after a first reignition A simulation of a multi-phase reignition on phase B and A show again a severe urrents and additional high frequeny urrent zeros; Figure 5 shows learly a peak values of 90 ka on phase B and 4 ka for phase A with a frequeny of almost KHz. These values are again far beyond the limit values given in standards. 4

5 Fig.5 Current observed on phase B and A after a multi-phase reignition Again, the grounded Wye onfiguration has been simulated with different values for the damping reator (mh, mh,,5mh and 5mH). In ase of learing a phases to ground fault, a maximum TRV has been observed also on phase B around,8 p.u. independently of the damping reator size. A first reignition on phase B give rise to TRV on phases A and C of : respetively,7 and,4 p.u. in ase of mh damping reator,,45 and,9 p.u. in ase of mh and,40 and,7 p.u. in ase of,5mh,,47 and,49 p.u. in ase of 5mH. As we see in Figure 6, with 5mH damping reator the produt frequeny urrent still around 6,x0 7 A.Hz the same value obtained for a multiphase reignition in ase of ungrounded Wye shunt apaitor bank and the onstraint still exeeding the limit value of x0 7 A.Hz. for a general purpose CB. Also, the zero rossing was not ompletely eliminated and two zero rossing were found before the first natural zero rossing. Fig. 7 TRV observed on eah phase of the iruit breaker As shown in the next figure, the transient voltage obtained after a reignition on phase A lead to signifiantly lower values then those obtained in ase of ungrounded shunt apaitor bank. In this ase we observed,5 p.u. on phase C and, p.u. on phase B. Fig.8 Transient voltage observed on phase C and B of the CB after a reignition on phase A The next figures 9 and 0 show learly that in ase of a phase to ground fault in presene of grounded apaitor bank, the total urrent when a reignition our on a phase is the sum of the soure short iruit urrent and the high frequeny urrent whih is the disharge of the shunt apaitor bank. The urrent in this ase has a peak value of 96 ka with a frequeny of almost khz. Also, in ase of multi-phase reignition no urrent is observed on the seond phase. Fig.6 Current observed for different values of damping reator after a reignition on phase B With a multi-phase reignition, the simulations show the presene again of the onstraints in term of urrent frequeny produt and the zero rossing. B. Case of phase to ground fault In this ase we observed as shown in Figure 7 the same TRV obtained in ase of ungrounded shunt apaitor bank: a maximum value of,47 p.u. on phase A with RRRV less than 0, kv/μs. Fig.9 Current observed on phase A after a first reignition Fig.0 Current observed on phase A and C after a multi-phase reignition 5

6 V. GROUNDED WYE CONNECTED SHUNT CAPACITOR BANK WITH VARISTOR IN PARALLEL WITH THE DAMPING REACTOR It was demonstrated through the simulation in previous setions that, both ases, the ungrounded and the grounded shunt apaitor banks represent an issue for general purpose CB present in a substation and in partiular oil iruit breaker beause of the severe high frequeny urrent with multiple zero rossing. Also explained is that the high frequeny of the urrent depends mainly on the resonane between the shunt apaitor bank and the damping reator following formula (). The zero rossing depend on two parameters, the high frequeny of the urrent and the fat that the urrent disharge from shunt apaitor bank is higher than the soure short iruit urrent. Inspired by the onfiguration of filters used in HVDC substation and to overome the onstraint mentioned previously we have deided to put in parallel with the damping reator a Metal Oxide Varistors (MOV) as shown in Figure. When onduting, the varistors will bypass the damping reator and will partially disharge the apaitor bank through the bus bar impedane. During the ondution period of the varistors, it is expeted that the iruit breaker see a very high peak urrent resulting from the disharge of the shunt apaitor bank and from the soure. When the varistors stops onduting, the damping reator returns in the iruit to disharge the remaining stored energy in the shunt apaitor bank. As explained in the previous paragraphs, sine the disharge urrent (outrush) of the shunt apaitor is muh lower than the short iruit urrent of the soure we an predit the elimination of the urrent zero rossing, and also lower peak urrent for that period of time. ZnO ZnO a ZnO ZnO b ZnO ZnO Séries reator 0.6 mh Q = A. Choie of varistors The varistors was modeled in EMTP-RV by using data from the buyer guide [7] for high voltage surge arrester. We have started with MCOV of 68 kv and dereased until obtaining satisfatory results in term of eliminating peak high frequeny urrent with multiple zeros rossing. These results will be presented in the next setions. B. Case of phases to ground fault As we see in Figure and explained in the introdution of this setion, the presene of the varistors in parallel with the damping reator have a great benefit in term of reduing onsiderably the number of zero rossing and dereasing the number of high peak urrents to be seen by the iruit breaker. Fig. Current observed on phase B and A after a multi-phase reignition We notie that the first urrent peaks, whih represent the ondution period of the varistors, have zeros rossing with very high di/dt observed, almost 500 A/µs. we presume that no iruit breaker will attempt to interrupt suh a very fast urrent variation. The next figures show a omparison between reignition urrents for different values of damping reator. We an learly see that there is no signifiant effet on the shape of the urrent, in terms of peak values and zero rossing, when raising the size of the damping reator above the value of 0.6mH used in the basi senario. XC 04 MVAR Fig. Grounded Wye shunt apaitor bank with MOV in parallel with the damping reator Fig. Current observed on phase B after a multi-phase reignition for different values of damping reator 6

7 Fig.4 Current observed on phase A after a multi-phase reignition for different values of damping reator C. Case of phase to ground fault In this ase the simulation was done with 0.6 mh as a damping reator. It is easy to predit that the high frequeny urrent will be attenuated and the number of zero rossings will be redued due to the presene of the varistors in parallel with the damping reator. Figures 5 and 6 show the shape of the urrent after a first reignition on the faulted phase. Fig.5 Current observed on phase A after a first reignition grounded and ungrounded shunt apaitor bank represent an issue for some tehnology of iruit breakers in ase of a multi-phase reignition beause of the multiple zero rossing and the urrent frequeny produt limits expressed in the standards. We have also notied that even with the inrease of the damping reator size the same issues persist. In ase of a reignition for a phase to ground fault we have notied an advantage for the ungrounded shunt apaitor bank where the high frequeny and the multiple rossing zeros quite less. The onfiguration with varistors seems to resolve the issue mentioned above where the zero rossing and the high frequeny urrent are onsiderably redued. We have notied also that the use of a bigger damping reator does not represent an advantage in this onfiguration. It is important to keep in mind that the onstraints explored in this paper ould represent a problem for some iruit breaker tehnology suh as the MOCB. VII. REFERENCES [] L. Van der Sluis, A.L.J. Jansen Clearing faults near shunt apaitor banks IEEE PES 990, Atlanta [] L. Van der Sluis, A.L.J. Jansen Controlling the transient urrents and overvoltage after the interruption of a fault near shunt apaitor banks International Conferene on Large High Voltage Eletri Systems 988, Paris [] A. Sabot, C. Morin, C. Guillaume, A. Pons, J.P. Taisne, G.Lo. Pizzo, H.U. Morf A unique multipurpose damping iruit for shunt apaitor bank swithing IEEE Transation on Power Delivery, Vol. 8, No., July 99 [4] Report by working group.4.7 of the IEEE Surge Protetive Devies Committee Impat of shunt apaitor banks on substation surge environment and surge arrester appliations [5] IEC High-voltage swithgear and ontrolgear- Part 00: Alternating-urrent iruit-breakers [6] IEEE C7.06 AC high-voltage iruit breakers rated on a symmetrial urrents basis [7] Parafoudres Haute tension, guide de l aheteur, ABB. [8] F. Martin, E. Jonquel Ciruit breaker tripping near apaitor banks CIGRÉ 006, Paris Fig.6 Current observed on phase A and C after a multi-phase reignition VI. CONCLUSIONS Transient simulation study was onduted for the purpose of evaluating the impat of the onfiguration of high voltage shunt apaitor banks on general purpose iruit breakers. In the ase of a phases to ground fault, both onfigurations, 7